PDF- -Control4 4K Ultra HD LU Series HDMI Matrix Switches Data Sheet - c4

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Chapter 4: Angle Modulation TRUE/FALSE 1

PM is another term for FM

ANS: F 2

the frequency of the modulated signal varies with the instantaneous amplitude of the modulating signal

ANS: T 3

Unlike AM,

the amplitude of an FM signal does not change with modulation

ANS: T 4

Similar to AM,

the power of an FM signal changes with modulation

ANS: F 5

Class C amplifier stages can be used throughout an FM transmitter

ANS: T 6

PM is often used to send digital data

ANS: T 7

A carrier can be frequency modulated with audio at the same time it is phase modulated with data

ANS: F 8

Mathematically,

an FM signal has an infinite number of sidebands

ANS: T 9

At certain modulation frequencies,

the power in the carrier frequency of an FM signal can go to zero

ANS: T 10

the modulation index depends on the frequency deviation

ANS: T 11

the modulation index depends on the frequency of the modulating signal

ANS: T 12

the modulation index cannot exceed one

ANS: F 13

the phase shift is proportional to the instantaneous amplitude of the modulating signal

ANS: T 14

A PM signal can be converted into an FM signal

ANS: T 15

Unlike AM,

a single modulating tone can produce many sidebands

ANS: T 16

more sidebands means more power

ANS: F 17

FM is sometimes called a constant-bandwidth communications mode

ANS: T 18

An FM signal is best looked at with a spectrum analyzer

ANS: T 19

An oscilloscope display will reveal much detail about an FM signal

ANS: F 20

There is no such thing as narrowband FM

ANS: F 21

the signal-to-noise ratio of a receiver's output can be better than that at the receiver's input

ANS: T 22

In the presence of noise,

an FM system exhibits an abrupt transition called "threshold effect"

ANS: T 23

Stereo FM signals produce a better signal-to-noise ratio at the receiver than mono does

ANS: F MULTIPLE CHOICE 1

The FM modulation index: a

increases with both deviation and modulation frequency b

increases with deviation and decreases with modulation frequency

decreases with deviation and increases with modulation frequency d

is equal to twice the deviation ANS: B 2

One way to derive FM from PM is: a

integrate the modulating signal before applying to the PM oscillator b

integrate the signal out of the PM oscillator c

differentiate the modulating signal before applying to the PM oscillator d

differentiate the signal out of the PM oscillator ANS: A 3

The bandwidth of an FM signal is considered to be limited because: a

there can only be a finite number of sidebands b

it is equal to the frequency deviation c

it is band-limited at the receiver d

the power in the outer sidebands is negligible ANS: D'4

Mathematically,

the calculation of FM bandwidth requires the use of: a

ordinary trigonometry and algebra c

Taylor series b

Bessel functions d

FM bandwidth can be approximated by: a

Armstrong's Rule b

Bessel's Rule

Carson's Rule d

ANS: C 6

NBFM stands for: a

National Broadcast FM b

Non-Broadcast FM

Near Band FM d

Narrowband FM

ANS: D'7

When FM reception deteriorates abruptly due to noise,

An FM receiver switching suddenly between two stations on nearby frequencies is called: a

Pre-emphasis is used to: a

increase the signal to noise ratio for higher audio frequencies b

increase the signal to noise ratio for lower audio frequencies c

increase the signal to noise ratio for all audio frequencies d

allow stereo audio to be carried by FM stations

ANS: A 10

A pre-emphasis of 75 µ s'refers to: a

the time it takes for the circuit to work b

the "dead time" before de-emphasis occurs c

the time delay between the L'and R channels d

the time-constant of the filter circuits used ANS: D'11

FM stereo: a

is implemented using an SCA signal

has a higher S/N than mono FM d

is not compatible with mono FM

ANS: A 12

An SCA signal: a

can use amplitude modulation b

ANS: D'13

The modulation index of an FM signal can be determined readily: a

using measurements at points where J0 equals one b

using measurements at points where J0 equals zero c

using measurements at points where the deviation equals zero d

only by using Bessel functions ANS: B COMPLETION 1

FM and PM are two forms of ____________________ modulation

ANS: angle 2

PM is extensively used in ____________________ communication

ANS: data 3

Compared to AM,

the signal-to-noise ratio of FM is usually ____________________

ANS: better 4

Compared to AM,

the bandwidth of FM is usually ____________________

ANS: wider greater 5

FM transmitters can use Class ____________________ amplifiers since amplitude linearity is not important

Both the power and amplitude of an FM signal ____________________ as modulation is applied

ANS: stay constant 7

the frequency deviation is proportional to the instantaneous ____________________ of the modulating signal

ANS: amplitude 8

The frequency deviation of an FM signal occurs at a rate equal to the ____________________ of the modulating signal

ANS: frequency 9

Mathematically,

the number of sidebands in an FM signal is ____________________

ANS: infinite 10

As FM sidebands get farther from the center frequency,

their power ____________________

ANS: decreases 11

Mathematically,

the value of an FM modulation index can be as high as ____________________

ANS: any number 12

as the modulating frequency decreases,

the modulation index ____________________

ANS: increases 13

as the frequency deviation decreases,

the modulation index ____________________

ANS: decreases 14

As the FM modulation index increases,

the number of significant sidebands ____________________

ANS: increases 15

For certain values of mf,

the amplitude of the carrier frequency ____________________

ANS: disappears goes to zero 16

The bandwidth of an FM signal can be approximated using ____________________ rule

ANS: Carson's 17

FM bandwidth can be calculated precisely using ____________________ functions

ANS: Bessel 18

The ____________________ effect is characteristic of FM reception in a noisy environment

ANS: threshold 19

The ____________________ effect is seen when an FM receiver is exposed to two FM signals that are close to each other in frequency

ANS: capture 20

Rest frequency is another name for an FM ____________________ frequency

ANS: carrier SHORT ANSWER 1

If a 2-volt instantaneous value of modulating signal amplitude causes a 10-kHz deviation in carrier frequency,

what is the deviation sensitivity of the modulator

If a 2-kHz audio tone causes a frequency deviation of 4 kHz,

What will be the deviation caused by a 3-kHz tone if the modulation index is 3

If the deviation sensitivity of an FM modulator is 2 kHz /V,

what will be the modulation index caused by a 1-volt,

At a modulation index of 2,

how much power is in the carrier of a 1000-watt FM transmitter

4 watts 6

At a modulation index of 2,

how much power is in the first pair of sidebands of a 1000-watt FM transmitter

At a modulation index of 2,

how much power is in the fifth pair of sidebands of a 1000-watt FM transmitter

ANS: 200 mW (0

2 watt) 8

Using Carson's rule,

what is the approximate bandwidth of an FM signal with a modulation index of 2 being modulated by a 5-kHz signal

Using the Bessel chart of Figure 4

what is the bandwidth of an FM signal with a modulation index of 2 being modulated by a 5-kHz signal if we ignore sidebands containing less than 1% of the total power

How would you use the fact that J0 is zero for certain known values of mf (2

etc) to measure the frequency deviation of an FM modulator

? ANS: Use an audio frequency generator to modulate the FM carrier

Using a spectrum analyzer,

adjust the audio frequency until the carrier amplitude vanishes

Record the audio frequency

Then do the calculation: δ = fm × mf where mf will have one of the known values

For example,

if fm is measured to be 2 kHz when mf is 5